1. Field of the Invention
The present invention relates to a fluorescence observation apparatus.
This application is based on Japanese Patent Application No. 2009-269156, the content of which is incorporated herein by reference.
2. Description of Related Art
In a known conventional method, a fluorescence image is divided by a reference image to acquire a quantitative fluorescence image in which a change in fluorescence intensity, depending on observation distance, has been corrected (for example, see the specification of U.S. Patent Application Publication No. 2008/0015446). In a fluorescence observation apparatus disclosed in the specification of U.S. Patent Application Publication No. 2008/0015446, the exposure time of an image acquisition device is further adjusted automatically to allow a reflected-light image and a fluorescence image to be observed at constant brightness even if the observation conditions are changed.
However, as in the conventional fluorescence observation apparatus, if the brightness of an image is controlled just by adjusting the exposure time, there is a disadvantage that, in some cases, an image having appropriate brightness cannot be observed because an image becomes bright even if the exposure time is set to a lower limit, or the intensity of excitation light for irradiating an observation target region is too high, thus fading a fluorescent dye contained in a living body, making the fluorescence image dark. There is a case in that, if the intensity of irradiation light is changed through light adjustment, the corrected fluorescence image does not become quantitative because of an effect caused when the irradiation-light intensity of excitation light and the irradiation-light intensity of illumination light are changed.